The invention relates to a method for operating a base station of a mobile radio system, to a corresponding signaling unit, a control unit, a mobile station, and a computer program.
Cellular mobile radio systems have a plurality of radio cells to which coverage is as a rule provided by in each case one base station. A known type of cellular mobile radio system is based on the GSM (Global System of Mobile communication) standard widely used in Europe and elsewhere. For what is termed the third mobile radio generation, cellular networks will in the future be constructed in Europe based on the UMTS-FDD (Universal Mobile Telecommunications Standard—Frequency Division Duplex) standard. Corresponding frequency bands have been allocated in Germany and elsewhere to the future carriers of UMTS-FDD networks. Each carrier has at least one frequency band for the upward direction (uplink) and one frequency band for the downward direction (downlink), referred to jointly as what are termed paired bands. It will also be possible to use an additional (non-paired) frequency band for the downlink. That is because owing to the asymmetry of future data services more transmission capacity will be needed on the downlink than on the uplink.
FIG. 1 shows a possible arrangement of the frequency bands allocated to two different carriers or, as the case may be, to their mobile radio systems. The first mobile radio system has been assigned a frequency band UL1 for the uplink and a frequency band DL1 for the downlink. The second mobile radio system has been assigned a frequency band UL2 for the uplink, a frequency band DL2 for the downlink, and a further frequency band DL3 for the downlink. The networks concerned are assumed to be two geographically overlapping cellular mobile radio networks operated using the cited frequency bands.
Since the frequency bands UL1, UL2 shown in FIG. 1 for the uplink and the frequency bands DL1, DL2 for the downlink have in each case a mutual band spacing bordering on zero, which is to say are directly adjacent to each other, and base stations of the two mobile radio systems can be located widely apart (which is to say the associated radio cells have a large radius), connections in one mobile radio system can be subject to disruptions due to connections in the other mobile radio system. For example, signals transmitted in the frequency band UL2 from a subscriber station of the second system to a corresponding base station of the second mobile radio system can influence the reception quality of a base station which belongs to the first system and receives signals from other subscriber stations in its radio cell in the uplink band UL1. Disrupting will occur particularly when the subscriber station of the second system is situated far from its base station, and so sends with high power, but is also located near the base station of the first system. Conversely, disruptions can occur at the subscriber station of the second mobile radio system owing to signals transmitted in the frequency band DL1 from the base station of the first mobile radio system for the reception of which signals in the second mobile radio system the frequency band DL2 has actually been provided within the second mobile radio system. Since a base station's maximum transmitting power exceeds a subscriber station's, the above-cited disruptions between the two overlapping mobile radio systems are greater on the downlink than on the uplink. That applies at least as long as the additional downlink frequency band DL3 is not being used by the second mobile radio system.
FIG. 2 shows the effect, in the case of strong disruptive influences, of this state of affairs on systems based on the UMTS-FDD standard. The subscriber station or, as the case may be, base station sending in the respective band is indicated in FIG. 2 below the frequency bands. Considered here are a subscriber station MS1 and base station BS1 of the first mobile radio system and a subscriber station MS2 and base station BS2 of the second system. If the subscriber station MS2 of the second system moves away from its own base station BS2, which belongs to the second mobile radio system and with which it is currently communicating, and in doing so moves toward the base station BS1 of the first system, then it will have to increase its transmitting power to continue ensuring an acceptable connection to its own base station BS2. Disruptions will in this way occur within the frequency band UL1 of the first mobile radio system owing to the base station BS1 of the first system receiving transmissions from its own subscriber stations MS1. However, the disruptions due to the transmissions of the base station BS1 of the first mobile radio system in the frequency band DL1 will simultaneously increase even more in the transmissions of the base station BS2 of the second mobile radio system in the frequency band DL2 on the downlink. That is because the transmitting power of the last-cited base station BS1 is in any event greater than that of the subscriber station MS2 of the second mobile radio system.
When the disruptions are very strong, the signal quality in the frequency band DL2 of the second system will initially be impaired so much owing to the stronger disruptive influence on the downlink compared to the uplink that reception will no longer be possible at the subscriber station MS2 of the second mobile radio system. This is indicated by the numeral 1 in FIG. 2 and by crossing out of the frequency band DL2 on the downlink of the second mobile radio system. Since transmitting from the subscriber stations to the respective base station is not allowed according to the UMTS-FDD standard without the reception of signals on the downlink, according to said standard the connection concerned will also be automatically disconnected on the uplink in the frequency band UL2. This is indicated in FIG. 2 by the numeral 2 and the corresponding arrow. Transmissions from the subscriber station MS2 of the second mobile radio system in the frequency band UL2 are in this way prevented from excessively impairing the reception of the base station BS1 of the first system in the frequency band UL1.
The mechanism just described will not function, however, if the frequency band DL2 that is symmetrical to or, as the case may be, paired with the frequency band UL2 is not used on the downlink for the connection to the subscriber station MS2 in the second mobile radio system but, instead, the non-paired band DL3 (see FIG. 1). Owing to the larger band spacing d between the frequency bands DL1 and DL3 of the two mobile radio systems there will now be a reduced likelihood of disruptions between the signals transmitted from the base stations BS1, BS2. Strong disruptions of the signals transmitted between the two mobile radio systems' subscriber stations MS1, MS2 and their base station is, though, still possible owing to the smaller band spacing between the two uplink frequency bands UL1, UL2. Said disruptions cannot, therefore, be avoided in the manner explained with reference to FIG. 2, so that negative influences on the operation or, as the case may be, reception of the base station BS1 of the first mobile radio system can be expected.